Interbody fusion grafts and instrumentation

ABSTRACT

This invention relates to implants formed from donor bone for use in lumbar interbody fusion procedures and instruments for performing such procedures. The implants are formed to include a concave surface formed from a portion of the medullary canal of a long bone. The concave surface defines a recess in the implant that serves as a depot for osteogenic material. Specific instruments for inserting the implants prepared according to this invention and for preparing the intervertebral space to receive the implants are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 10/645,413, filed on Aug. 21, 2003, which is a divisional ofU.S. patent application Ser. No. 09/698,623, now U.S. Pat. No.6,610,065, filed on Oct. 27, 2000, which is a divisional of U.S. patentapplication Ser. No. 09/181,353, now U.S. Pat. No. 6,174,311, filed onOct. 28, 1998 each of which are hereby incorporated by reference intheir entirety.

FIELD OF THE INVENTION

The present invention relates to implants for use in lumbar interbodyfusion procedures and instruments for performing such procedures. Morespecifically, this invention relates to implants formed from donor bonethat are useful to restore disc height and promote bone fusion afterdiscectomy and to instruments and methods for preparing theintervertebral space and inserting the implant into an intervertebralspace.

BACKGROUND OF THE INVENTION

One of the leading causes of lower back pain and disability results fromthe rupture or degeneration of one or more lumbar discs in the spine.Pain and instability are caused by compression of the spinal nerve rootsbecause the damaged discs protrude into the vertebral canal and do notprovide sufficient biomechanical support for the full range of vertebralmotion. Normally intervertebral discs, which are located betweenendplates of adjacent vertebrae, stabilize the spine and distributeforces between the vertebrae and cushion vertebral bodies. Anintervertebral disc includes a semi-gelatinous component (the nucleuspulposus) and a fibrous ring (the annulus fibrosis). The spinal discsmay be displaced or damaged due to trauma, disease, or aging. Aherniated or ruptured annulus fibrosis may result in nerve damage, pain,numbness, muscle weakness, and even paralysis. Furthermore, as a resultof the normal aging processes, discs dehydrate and harden, therebyreducing the disc space height and producing instability of the spineand decreased mobility.

Not all patients with damage or spinal deformities require surgicalintervention. However, patients who have failed to respond toconservative treatment and who have demonstrable disc pathology oftenrequire surgical correction. Most typically the surgical correctionincludes a discectomy (surgical removal of a portion or all of theintervertebral disc). Discectomy is often followed by fusion of theadjacent vertebrae. To alleviate the pain, abnormal joint mechanics,premature development of arthritis, and nerve damage, the disc spacevacated by the damaged disc must be preserved following discectomy.Therefore, spacers or implants are required between the vertebrae thatwere adjacent to the resected disc.

Current treatment methods have been unable to accurately control theendplate removal using conventionally designed chisels, scrapers, andcutters. Use of conventional surgical instruments does not adequatelycontrol the depth of the cut into the disc space or provide a means toaccurately countersink the implant into the prepared cavity—particularlyfor non-threaded impacted implants. Furthermore, current methodologiesdo not provide sufficient protection of the neural structures duringsurgery to prevent neural injury

Current treatment methods utilize grafts, either bone or artificialimplants, to fill the intervertebral space between adjacent vertebrae.It is desirable that these implants not only fill the disc space vacatedby the damaged disc but also restore the disc space height topre-damaged condition. An implant must be sufficiently strong to bearsubstantially all the body's weight above the vertebral space where itis inserted. Furthermore, it is desirable to use the implants to promotefusion of the adjacent vertebrae across the disc space and therebypromote mechanical stability. Current methodologies use implants orspacers made of metal, plastic composites, or bone. Use of bone implantsoffers several advantages over artificial spacers or implants. The bonesprovide an implant having a suitable modulus of elasticity that iscomparable to that of the adjacent vertebrae. The bone implants can beprovided with voids, which can be packed with cancellous bone or otherosteogenic material to promote bone growth and eventual fusion betweenadjacent vertebrae. Furthermore, implants formed from cortical bone havesufficient compressive strength to provide a biomechanically soundintervertebral spacer while it is slowly being incorporated or absorbedby the body and substituted for the patient's own bonetissue—colloquially referred to as “creeping substitution.”

While it is desirable to use natural bone grafts as implants, use ofbone is often limited because of a small supply of suitable sources.Xenografts from non-humans (animals) suffer from rejection problems onceimplanted. While measures are being taken to limit the human body'srejection of xenografts, greater success is still achieved with boneobtained from human sources. The best source is an autograft from thepatient receiving the graft. Removal of an autograft requires furthersurgery and is limited in amount and structural integrity by thepatient's anatomy. The alternative source of human bone grafts isallografts harvested from human donors. Since the number of peopledonating tissue to science is small, these bone grafts represent anextremely valuable and rare commodity. Current methodologies forproviding cortical bone implant spacers typically require cutting thespacer, usually in the form of a round dowel, from the diaphysis of along bone. Only a certain portion of the diaphysis is sufficiently thickto provide dowels with requisite strength to maintain the intervertebralspace. For example, in a human femur, only about the middle third of thediaphysis, where the shaft is narrowest and the medullary canal is wellformed, has sufficient bone wall thickness and density to be used toprepare cortical dowels. The suitable portions of the diaphysis aresliced, and a plug is then cut from each slice. The plugs are thenmachined to form a round dowel. Most often the dowel includes themedullary canal to provide a depot for osteogenic material and promotefusion of the adjacent vertebrae. Much of the donor bone is wasted,particularly the remnants of the slices from the diaphysis used toprovide the dowels as well as the end portions of the long bone whichcannot be utilized. Above and below this middle section of thediaphysis, the walls of the femur bone become thinner because of theseparation of the layers of the bone into cancelli. Thus, these portionsof the femur are not considered suitable for forming cortical dowelshaving the required dimensions for inserting into vertebral spaces. Useof these remnants would provide a more efficient use and conservation ofa limited and very valuable natural resource of cortical bone.

Thus, there remains a need for improved bone graft implants andinstruments for their placement in the body.

SUMMARY OF THE INVENTION

Thus, there is provided with the present invention an implant preparedfrom bone. The implant has a shaped body and sufficient length to extendfrom an anterior portion of a vertebral body to a posterior portion anda height sufficient to separate adjacent vertebrae. The implantcomprises a bone portion having an upper and lower bone engagingsurface, a first sidewall, and an opposite second sidewall. The firstand second sidewalls extend between the upper and lower bone engagingsurfaces. Furthermore, the first sidewall includes a portion defined bya concave surface. Preferably, the implant also includes a recessedregion that serves as a depot or receptacle for deposition of osteogenicmaterial to enhance bone growth and eventual fusion of the adjacentvertebrae. One end of the implant is provided with structural featuresto engage an implant holder. In a preferred embodiment, the other end ofthe implant is provided with a shape to ease insertion into theintervertebral space. The implant prepared according to the presentinvention has sufficient biomechanical support to maintain the desiredintervertebral space while it is gradually being replaced with new bonegrowth. In specific embodiments of the present invention, the implant isprovided in the form of a J-shape; in other specific embodiments, theimplant is provided in the form of a crescent shape.

There is also provided in accordance with the present invention animplant holder. The implant holder includes a gripping head forreleasably securing the implant. Preferably the impact holder alsoincludes an impacting surface for driving the implant into a preformedcavity in the intervertebral space. The gripping head includes at leastone implant engaging structural feature, such as a pin. Optimally, thepin includes at least a radiopaque portion to provide a means forviewing placement of the implant via radiography during surgery. In oneembodiment, the gripping head on the implant includes a surfacepreferably roughened or knurled to secure the implant into the preformedcavity. In another embodiment of the present invention, the implantholder including the gripping head includes at least two surfaces. Eachof the surfaces includes a pin that releasably secures the implant tothe gripping head by matingly engaging recesses in the implant. Theimplant holder of the present invention securely holds the implant sothat it can be impacted into the preformed cavity in the intervertebralspace and then releases the implant so it remains in the cavity.

There is also provided in the present invention instruments forpreparing an intervertebral space for receiving the final fusionimplant. The instruments include a chisel for preparing theintervertebral space to receive the implant, preferably by cutting acavity in the opposing endplates of adjacent vertebrae. The bone chiselincludes at least two cutting edges. The bone chisel also includesopposing curved surfaces extending distally beyond the cutting surfaceto center the chisel and the cutting edges between the opposing surfacesof adjacent vertebrae. When the chisel and cutting blades are centeredbetween the opposing surfaces, the blades cut equally from bothsurfaces.

Other instruments included for use in the present invention includescrapers, rotating scrapers, and impacting or “slap” hammers for drivingthe implants into position. The slap hammer allows for controlledimpacting force and removal of the chisel after cutting.

Another aspect of the present invention includes a nerve retractor bladeassembly for manipulation of neural structures such as the dural sac andtraversing nerve root with minimal trauma to the respective structures.The assembly includes a retractor having a channel adapted to receive aretractor blade, and further can include at least one pin, preferablytwo pins, for securely fixing the positioning of the retractor assemblyand blade proximal to the intervertebral space. The blade can be adaptedfor engagement with the retractor and then for extending into theintervertebral space to provide anchorage proximal to the disc space,maintain disc height, and maintain distraction. The nerve retractor alsoincludes a handle attached at an angle to the channel. In a preferredembodiment, the retractor channel is provided in the form of a concavechannel. It is also contemplated that the retractor channel can beformed in a variety of other shapes, for instance, rectangular andbroadened V-shaped channels are also included within the presentinvention.

Yet another aspect of the present invention includes a protective guidesleeve. The protective sleeve includes a body having a hollow core forreceiving instruments for performing surgery. In addition, theprotective sleeve provides a narrow but unobstructed passageway to theintervertebral space and minimizes the area of tissue impacted by thesurgery. Preferably the protective sleeve includes a first and a seconddistractor fin that can be inserted into the intervertebral space tomaintain the space height and alignment of the vertebrae. The protectivesleeve provides protection for neural structures and preventsencroachment of the neural structures into the surgical area. Theprotective sleeve allows use of a depth stop on surgical tools.Preferably, the protective sleeve includes at least one window tofacilitate visualization. The instruments for preparing and insertingspinal fusion implants can be received within the protective sleeve.Such instruments include the implant holder engaged to an implant andthe bone chisel, scrapers, and drills provided in the present invention.

Accordingly, it is one object of the present invention to provide animproved implant of bone to maintain an intervertebral space afterdiscectomy.

It is another object of the present invention to provide an implantholder to releasably secure the implant and facilitate impaction of theimplant into position within the intervertebral space.

It is still another object of the present invention to provide a cuttingchisel to prepare a cavity in the intervertebral space between twoopposing adjacent endplates on vertebrae.

It is yet another object of the present invention to provide a retractorfor manipulation of neural structures.

Further objects, features, benefits, aspects, and advantages of thepresent invention shall become apparent from the detailed drawings anddescriptions provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of an implant accordingto the present invention.

FIG. 2 is a side view of the implant of FIG. 1.

FIG. 2 a is an enlarged view of a portion of the side of the implant ofFIG. 2 illustrating the ridges for engaging bone.

FIG. 3 is a top elevated view of the spacer of FIG. 1.

FIG. 4 is an end view of the tool engaging end of the implant of FIG. 1.

FIG. 5 is a side sectional view of an implant revealing the toolreceiving slots and recesses.

FIG. 6 is an end view of the insertion end of implant of FIG. 1.

FIG. 7 is an elevated top view of one embodiment of an implant holderaccording to the present invention.

FIG. 8 is an end view of the implant holder of FIG. 7.

FIG. 9 is a side view of the implant holder of FIG. 7.

FIG. 10 is a perspective view of the holder of FIG. 7.

FIG. 11 is a cutaway view of an intervertebral space that includes animplant seated within the intervertebral space and seating a secondimplant using the implant holder of FIG. 7.

FIG. 11 a is a cutaway view of an intervertebral space that includes acrescent shaped implant seated within the intervertebral space andseating a second implant using an implant holder.

FIG. 12 is a perspective view of an alternative embodiment of a J-shapedimplant according to the present invention.

FIG. 13 is side view of the implant of FIG. 12.

FIG. 14 is an elevated top view of the implant of FIG. 12.

FIG. 15 is an end view illustrating the tool attachment end of theimplant of FIG. 12.

FIG. 16 is an end view illustrating the insertion end of the implant ofFIG. 12.

FIG. 17 is an elevated top view of an alternative embodiment of animplant holder according to the present invention for use with theimplant of FIG. 12.

FIG. 17 a is an enlarged view of a gripping head of the implant holderof FIG. 17.

FIG. 18 is a side view of the implant holder of FIG. 17.

FIG. 18 a is an enlarged top view of the gripping head of the implantholder of FIG. 17.

FIG. 18 b is a first end view of the implant holder of FIG. 17.

FIG. 19 is a side view of the implant of FIG. 12 engaged to the implantholder of FIG. 17.

FIG. 20 a is an elevated top view of the implant of FIG. 12 engaged tothe implant holder of FIG. 17.

FIG. 20 b is a first end view of the implant of FIG. 12 engaged to animplant holder of FIG. 17.

FIG. 21 is a perspective view of an implant of FIG. 12 engaged to animplant holder of FIG. 17.

FIG. 22 is a perspective view of another alternative embodiment of acrescent-shaped implant according to the present invention.

FIG. 23 is a perspective view of another alternative embodiment of animplant holder according to the present invention.

FIG. 23 a is an enlarged perspective view of the gripping head of theimplant holder of FIG. 23.

FIG. 24 is a perspective view of the implant of FIG. 22 engaged to theimplant holder of FIG. 23.

FIG. 25 is a perspective view of one embodiment of a chisel according tothe present invention.

FIG. 25 a is an enlarged perspective view of the cutting head of thechisel of FIG. 25.

FIG. 25 b is a side sectional view of three lumbar vertebrae and thechisel of FIG. 25 as it is initially inserted into the intervertebralspace.

FIG. 25 c is a side sectional view of three lumbar vertebrae and thechisel of FIG. 25 cutting the opposing surfaces of adjacent vertebrae.

FIG. 25 d is a side sectional view of three lumbar vertebrae and thechisel of FIG. 25 after completing the initial cavity formation in theintervertebral space.

FIG. 26 is a perspective view of a bone shaver according to the presentinvention.

FIG. 26 a is a perspective view of the cutting head of the bone shaverof FIG. 26.

FIG. 27 is a perspective view of one embodiment of a slap hammer for usewith the present invention.

FIG. 28 is a perspective view of one embodiment of a nerve retractorassembly according to the present invention.

FIG. 29 is a perspective view of a retractor holder illustrated in FIG.28.

FIG. 29 a is a partial perspective view of the back of the support bladefor the retractor of FIG. 29.

FIG. 30 is a perspective view of the retractor blade for the retractorof FIG. 29.

FIG. 30 a is a partial perspective view of the lead tip of the retractorblade in FIG. 30.

FIG. 31 is a perspective view of one embodiment of a distractor for usewith the present invention.

FIG. 31 a is a partial perspective view of the distractor tip of thedistractor depicted in FIG. 31.

FIG. 32 is a perspective view of a round scraper for use in the presentinvention.

FIG. 32 a is a partial perspective view of the scraper head of the roundscraper depicted in FIG. 32.

FIG. 32 b is a side view of the round scraper of FIG. 32.

FIG. 32 c is an elevated top view of the round scraper of FIG. 32.

FIG. 32 d is a partial perspective view of the scraper head of the roundscraper of FIG. 32.

FIG. 32 e is an elevated top view of the scraper head of the roundscraper of FIG. 32. FIG. 32.

FIG. 32 f is a side view of the scraper head of the round scraper ofFIG. 32.

FIG. 33 is a perspective view of a plane scraper for use in the presentinvention.

FIG. 33 a is a partial perspective view of the scraper head of the planescraper depicted in FIG. 33.

FIG. 33 b is a side view of the plane scraper of FIG. 33.

FIG. 33 c is an elevated top view of the plane scraper of FIG. 33.

FIG. 34 is a perspective view of a rotatable cutter for use with thepresent invention.

FIG. 34 a is a partial perspective view of the cutting head of therotatable cutter depicted in FIG. 34.

FIG. 34 b is an elevated top view of the rotatable cutter of FIG. 34.

FIG. 34 c is a side view of the rotatable cutter of FIG. 34.

FIG. 34 d is a first end view of the rotatable cutter of FIG. 34.

FIG. 35 is a perspective view of a toothed scraper according to thepresent invention.

FIG. 35 a is a partial perspective view of the cutting head of thetoothed scraper depicted in FIG. 35.

FIG. 36 is a perspective view of one embodiment of a guide sleeve forreceiving surgical instruments and implantation instruments according tothe present invention.

FIG. 37 a is a perspective view of an alternative embodiment of a chiselfor use in the present invention.

FIG. 37 b is an elevated top view of the chisel in FIG. 37 a.

FIG. 37 c is a side view of the chisel in FIG. 37 a.

FIG. 38 is a side view of the chisel depicted in FIG. 37 a receivedinside the guide sleeve depicted in FIG. 36.

FIG. 39 a is a perspective view of an alternative embodiment of animplant holder.

FIG. 39 b is an elevated top view of the implant holder depicted in FIG.39 a.

FIG. 39 c is a side view of the implant holder depicted in FIG. 39 a.

FIG. 39 d is a cross-sectional view of the implant holder depicted inFIG. 39 a.

FIG. 39 e is an enlarged view of the gripping head of the implant holderdepicted in FIG. 39 a.

FIG. 39 f is a perspective end view of the gripping head of the implantholder depicted in FIG. 39 a.

FIG. 40 a is a perspective view of an implant inserter according to thepresent invention.

FIG. 40 b is an elevated top view of the implant inserter depicted inFIG. 40 a.

FIG. 40 c is a side view of the implant inserter depicted in FIG. 40 a.

FIG. 41 is a perspective cutaway view of a bone graft loader accordingto the present invention.

FIG. 42 is a perspective cutaway view of the bone graft loader of FIG.41 as the piston has been received in the loader shaft.

FIG. 43 a is a top cutaway view of an intervertebral space that includesthe bone graft loader of FIG. 41 loaded with osteogenic materialreceived within a protective sleeve and positioned in the intervertebralspace.

FIG. 43 b is a top cutaway view of an intervertebral space and the bonegraft loader of FIG. 41 delivering osteogenic material into theintervertebral space.

FIG. 44 a is a top sectional view of an idealized diaphysis section of along bone illustrating a bone section useful for forming a cortical bonedowel.

FIG. 44 b is a side view of an idealized section from the diaphysis of along bone illustrating the medullary canal and a portion of the bonetissue useful for forming a cortical bone dowel of the prior art.

FIG. 44 c is a perspective view of a cortical bone dowel formed from thediaphysis section of 44 a.

FIG. 45 is an elevated top view of the remnant of the bone section fromFIGS. 44 a and 44 b.

FIG. 46 is a perspective view of the bone remnant from FIGS. 44 a and 44b.

FIG. 47 is a top sectional view of an upper portion of the diaphysis ofa humeral shaft illustrating various bone implants that can be formedfrom the bone section.

FIG. 48 is a top sectional view of an upper portion of the diaphysis ofa tibial shaft illustrating various bone implants that can be formedfrom the bone section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of thepresent invention, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is intended thereby. Any alterations andfurther modification in the described processes, systems, or devices,and any further applications of the principles of the invention asdescribed herein are contemplated as would normally occur to one skilledin the art to which the invention relates.

This invention provides bone implants for insertion into theintervertebral spaces between adjacent vertebrae following discectomy.The bone implants are useful for maintaining and/or restoring a desiredspacing between adjacent vertebrae. The bone implants of the presentinvention include a recessed area that serves as a depot for receivingosteogenic material, thereby enhancing bone ingrowth and fusion of theadjacent vertebrae. The implants of the present invention are designedto conserve donor bone material without compromising necessarybiomechanical properties of the implant to support the forces generatedat the implantation level. Multiple implants according to the presentinvention may be formed from a single donor bone. Further, the implantsaccording to the present invention may be obtained from remnants ofdonor bone utilized to form alternative implants and from the upper andlower end portions of the diaphysis of long bones lacking the requiredproperties for cylindrical dowels, collectively referred to herein as“remnants.” Preferably, each implant includes at least a portioninfluenced by the shape of the medullary canal. Preferably, themedullary canal is included as a curved surface in the body of theimplant that can serve as a depot for osteogenic material. Optimally,the design of the implant includes surface features which inhibitexpulsion of the implant from the preformed cavity.

Referring now to FIG. 1 through FIG. 6, one embodiment of an implantaccording to the present invention is illustrated. Implant 10 includesbody 11 having a concave surface 14 that defines a recessed area 15 intobody 11. Implant 10 further includes a tool attachment end 32 adaptedfor engagement with an implant holder. Tool attachment end 32 caninclude a variety of recesses, receptacles, grooves, slots, projections,and other supporting members to engage corresponding surface features onan implant holder. Implant 10 also includes an insertion end 17. On theimplant illustrated in FIGS. 1-6, the insertion end is defined by curvedsurface 18. It is understood that curved surface 18 can also includesurfaces having a uniform and non-uniform curvature and tapered ends forincreasing the ease of insertion of the implant into the intervertebralspace.

Body 11 of implant 10 is substantially elongated and defines alongitudinal axis 19. The length of the implant 11 is sufficient toprovide sufficient support and stability to the spinal column. Typicallythe implant has a length of about 21 mm to about 27 mm, more preferablyabout 22 to about 26 mm. When viewed from the side, the height ofimplant 10 can be substantially uniform for its entire length, whichlies parallel to the longitudinal axis. Alternatively, as illustrated inFIG. 2, the height of implant 10 can vary along its length. The maximumheight of implant 10 is about 11 mm to about 15 mm in height as shown byreference line 21. The lesser height 23 of implant 10 is about 7 mm toabout 11 mm. The maximum width 25 of implant 10 may not exceed the widthof the bone remnants, which serve as the source of donor bone for theimplants. However, the implant is formed with a sufficient maximum widthto adequately support the forces generated at the site of implantationand to provide stability to the implant to inhibit rotation in the discspace. Furthermore, in preferred embodiments, the width of the implantis sufficient to withstand a downward applied compressional force ofabout 30,000 Newtons. The width of the implant is about 8 mm to about 14mm, more preferably about 10 mm to about 12 mm.

The outer surface of implant 10 can include surface features such asridges or teeth to prevent retropulsion of the implant from theintervertebral space. Ridges 12 can be randomly or uniformly distributedabout the outer surface of implant 10. The ridges 12 can be distributedon one, two, three, or four sides of the exterior surface of implant 10.Preferably, ridges 12 and 13 are located on the upper surface 40 andlower surface 42, respectively. Ridges 12 and 13 are defined as anequilateral triangle defining an angle of about 50° to about 70° at theapex and having a height of about 1 mm.

Body 11 of implant 10 includes a recessed area 15 that can be used forreceiving osteogenic material. One side of implant 10 includes concavesurface 14 formed as a result of the medullary canal of the long bone.While concave surface 14 generally follows the contours of the medullarycanal of the donor bone, it will be understood that cleaning andpreparing the bone graft from the donor may slightly alter the medullarycanal, thereby altering the configuration of concave surface 14.Moreover, concave surface 14 typically resembles a portion of acylindrical wall. However, the specific configuration of the surface mayvary, depending on the shape of the medullary canal in the donor bone.Concave surface 14 defines a recessed area 15. In addition to concavesurface 14, the implant can include other apertures such as apertures 20and 22. In preferred embodiments, apertures 20 and 22 extend throughimplant 10 and are sized to receive a sufficient amount of an osteogenicmaterial to promote bone ingrowth and fusion of the adjacent vertebrae.

Implant body 11 includes a substantially flat side 16 opposite concavesurface 14. Flat side 16 adjoins tool engagement end 32 and extendsalong the length of body 11 to abut insertion end 17. It is understoodfor the purposes of this invention that flat side 16 is substantiallyplanar. However, it is also within the scope of the present inventionthat flat side 16 can include a curved surface, if desired.

Tool attachment end 32 can include a variety of recesses, apertures, andother structural features to engage an implant holder. For example, asdepicted in FIGS. 4 and 5, tool engagement end can include slots 24, 26,first indent 28, and second indent 30. First indent 28 and second indent30 can be provided to matingly engage corresponding pins on an implantholder.

Insertion end 17, which includes rounded surface 18 is depicted in FIG.6. It is desirable, but not necessary, that rounded end 18 defines auniform curvature as depicted in FIG. 6. It is desirable to round overor streamline the end of implant body 10 to ease the insertion of theimplant into a preformed cavity. Therefore, in addition to curvedsurface 18, the implant also includes incline surfaces 34 and 36.Inclined surfaces 34, 36 and curved surfaces 18 may be provided tofacilitate insertion of the implant into the preformed cavity. Asexplained further herein, such curved end surfaces obviate the necessityto square off the bottom of the channel of the preformed cavity.

Also provided with the present invention is an implant holder forreleasably securing and impacting the implant of FIGS. 1-6 into thepreformed cavity. One embodiment of the implant holder is depicted inFIGS. 7-10. Implant holder 50 includes handle 70, gripping head 59,first branch 52 engaged to handle 70, and second branch 54. Secondbranch 54 is pivotally attached to first branch 52 with pivot pin 56.Gripping head 59 includes a first gripping arm 60 integral to secondbranch 54 and a second gripping arm 62 integral to first branch 52.Thus, in preferred embodiments, gripping arm 62 remains stationary whilegripping arm 60 pivots on pivot pin 56 to provide access to a recesscavity 68 formed between opposing gripping arms 60 and 62. Gripping arms60 and 62 include projections 64 and 66, respectively. Projections 64and 66 are adapted to matingly engage first indent 28 and second indent30 on implant 10. Furthermore, gripping head 59 includes a surface forcontacting tool engaging end 32 of implant 10 and to drive the implantinto a preformed cavity. In the preferred embodiment illustrated inFIGS. 7-10, gripping arms 60 and 62 include impacting surfaces 61 and63, respectively. Impacting surface 61 abuts and is substantiallyorthogonal to the interior side of gripping arm 60. Impacting surface 63is similarly disposed on gripping arm 62.

Opposite end of gripping arms 60 and 62 are first branch 52 and a secondbranch 54, respectively. First branch 52 is connected to handle 70 andremains stationary along with gripping arm 62. However, second branch 54on the opposite end of gripping arm 60 opens by pivoting on pivot pin56. Pivoting of branch 54 on pivot pin 56 causes gripping arm 60 to moveaway from gripping arm 62 and thus open the recessed cavity 68 toreceive tool engaging end 32 of implant 10. After receiving toolengaging end 32, second branch 54 is then pivoted towards first branch52 to close recess cavity 68 and securely engage the projection 64 and66 into first and second attachment recesses 24 and 26 and first andsecond indents 28 and 30 on implant 10.

Once branching arm 54 abuts or nearly abuts branching arm 52, lockingpin 58 engages first branch 52 and prevents pivoting of second branch54. Implant 10 can be released from implant holder 50 by disengaginglocking pin 58 and pivotally opening second branch 54 from first branch52. Alternatively, other locking means such as a slidable sleeve or acollet that are adapted to encircle first and second branches 52 and 54and prevent opening of the gripping arms 60 and 62 can be used with thepresent invention. While locking pin 58 is illustrated in FIGS. 8-10 asone embodiment of securely engaging implant 10, it is contemplated thatother locking means or mechanisms known to those skilled in the art canbe used with the present invention.

Implant holder 50 engaged to implant 10 can be used to insert theimplant into the intervertebral space as depicted in FIG. 11. Insertiontube 90 is inserted into disc space 82 in a far lateral PLIF approachthat can be used with a transforminal procedure. Implant 10 a isdepicted as fully seated in a first preformed cavity adjacent tovertebral body 80. In a preferred embodiment, insertion tube 90 is firstpositioned adjacent the preformed cavity. Insertion tube 90 is adaptedto slidably receive implant 10 and implant holder 50. After implant 10is securely engaged in the preformed cavity, locking pin 58 is released,thereby allowing second branch 54 to pivot away from first branch 52 andrelease engagement of projections 64, 66, and gripping arms 60 and 62from the corresponding attachment recesses and indents on implant 10.Insertion tube 90 may be sized to permit movement of the branchestherein or may be withdrawn to allow sufficient movement fordisengagement. Implant holder 50 and insertion tube 90 are then removed.

In FIG. 11 a, a crescent implant and an implant holder disposed withinthe disc space are illustrated. A first implant 210 a is depicted asseated in the disc space 82. Insertion tube 90 provides access to thedisc space 82 from the posterior side of the vertebral body 80 forinsertion of implant 210. Recessed areas 219 on implants 210 and 210 aare disposed medially.

An alternative embodiment of an implant prepared according to thepresent invention is depicted in FIGS. 12-16. Implant 110 is formed inelongated J-shaped body 111 that defines a longitudinal axis 119. Oneside of J-shaped body 111 includes curved section 122 that adjoins J-end128 to form the crook of the J-shape and is bounded by straight section120 opposite J-end 128. In a preferred embodiment, curved section 122includes internal concave surface 114. Preferably, concave surface 114is contoured based on the medullary canal of a long bone. Straightsection 120 abuts tool attachment end 132. Tool attachment end 132includes tool engagement recess 124 for securely engaging an implantholder. Tool engagement recess 124 is adapted to secure implant 110 inthe implant holder to minimize vertical movement of the implant whilethe implant is being inserted into preformed cavity. It is contemplatedthat the tool engagement end 132 can further include a variety of toolengagement structures, such as grooves, receptacles, holes, recesses,projections, pins, and detents. Upper tool recess 126 is disposedbetween tool engagement end 132 and flat side 116. Flat side 116, whichis opposite straight section 120, defines the back or a laterallydisposed portion of J-shaped body 111 and abuts insertion end 117 on oneend and on the opposite end abuts shoulder 127. Insertion end 117includes curved surface 118. While not specifically illustrated in FIGS.12-16, implant 11 is provided to have a length, height, and width asdescribed for implant 10.

A plurality of ridges 112 and 113 are provided on the top surface 129and bottom surface 130 of implant 110. It is more or less depicted thattop surface 129 and bottom surface 130 include a series of ridges 112and 113. However, it is contemplated that ridges can be defined on one,two, three, or four sides of implant 110.

An alternative preferred embodiment of an implant holder is illustratedin FIGS. 17-21. Implant holder 150 includes a shaft 151 that defines alongitudinal axis 164. The shaft 151 includes gripping head 152 on oneend and coupling point 153 on the opposite end. The shaft splits into anupper branch 154 and a lower branch 156. The upper and lower branchesare separated by channel 158. Upper branch 154 includes upper branchextension 160, and lower branch 156 includes lower branch extension 170.Collectively, upper branch extension 160 and lower branch extension 170define the gripping head 152.

The gripping head 152 includes at least one implant engaging structure.Preferably gripping head 152 also includes taper ends 166 and 168 thatengage in corresponding recesses in the implant. The projections areprovided to control lateral and vertical motion as the implant isimpacted into the intervertebral space. Optimally, gripping head 152also includes a surface that can be used to impact or drive the implantin the preformed cavity.

In preferred embodiments, the gripping head 152 illustrated in FIGS.17-21 includes upper and lower branch extensions 160 and 170,respectively. Upper branch extension 160 includes incline surface 162,which is provided to matingly engage with straight section 120 onimplant 110. Branch extension 160 includes tapered end 166 that matinglyengaging tool engagement recess 124. Lower branch extension 170 includesend 172 for engaging shoulder 127 on implant 110. Furthermore, lowerbranch extension 170 includes tapered end 168 which, along with taperedend 166, is provided for engaging tool engagement recess 124. Taperedends 166 and 168 engage in tool recess 124 to prevent lateral movementof the implant during impacting to force the implant into the preformedcavity.

As shown in FIG. 19, the shaft also includes outer sleeve 184, which ismoveable along the shaft in a direction parallel to the longitudinalaxis and urges the upper and lower branches together when the outersleeve 184 is moved in the direction toward gripping head 152. Movementof outer sleeve 184 is controlled by the threaded engagement of threadednut 182 with external threads 157. Outer sleeve 184 includes an internalsurface (not shown) adapted to engage inclined surfaces 155 and 159 onthe inner shaft to urge the branches together.

Moving outer sleeve 184 on shaft 151 toward the gripping head 152 urgesupper and lower branches 154 and 156 and upper and lower branchextensions 160 and 170 toward each other. Thus, upper and lower branchesclamp and secure an implant in the gripping head.

Coupling point 153 is included on shaft 151 opposite from gripping head152. Coupling point 153 is used to attach a handle 180 or an impactingtool to drive an included implant in to preformed cavity.

In FIGS. 19-21, implant 110 is depicted mounted in implant holder 150.Upper and lower branch extensions 160 and 170 clamp implant in grippinghead 152. FIG. 20 a and 21 illustrate the implant engaged in an implantholder. The implant and holder are superimposed on top of an idealizedoutline of the superior surface of a lumbar vertebra body. The implantis positioned to lie inside the lateral edges of the vertebral body. Theconcave area is positioned to face medially. A second implant may bepositioned on the opposite side of the vertebral body. The concave areasof the two implants would face each other to form a enclosed area toserve as a depot for osteogenic material.

Yet another embodiment of an implant according to the present inventionis depicted in FIG. 22. Implant 210 includes crescent-shaped body 211having a convex surface 217 and an opposite concave surface 215. Convexsurface 217 is disposed between tool-engaging end 222 and oppositeinsertion end 216. Implant 210 is depicted as having a series of ridges212 projecting out of upper surface 214 and similar ridges 213projecting from the lower surface for engaging bone surfaces. It isunderstood that implant 210 can be prepared having a fewer number ofridges than depicted in FIG. 22. For example, implant 210 can includesurfaces having no ridges, or ridges on one, two, three, or four or moresurfaces. Implant 210 is provided with a length, height, and width as isgenerally described for implant 10.

Concave surface 215 abuts surface wall 226 and on an opposite endadjoins taper surface 220. While concave surface 215 gradually followsthe contours of the medullary canal, it is understood that cleaning andmachining the bone graft from a donor may slightly alter the medullarycanal, thereby altering the configuration of concave surface 215.Preferably, a portion of concave surface 215 is formed from a section ofthe medullary canal of a long bone. Concave surface 215 defines arecessed area 219 that serves as a depot for osteogenic material.

Insertion end 216 is provided to increase the ease of insertion of theimplant into a preformed cavity. Thus, it is within the scope of thisinvention to provide insertion end 216 having a substantiallystreamlined shape. For example, insertion end 216 can include a bulletshape, a curved shape, a frustoconical shape, and/or a conical shape. Inthe preferred embodiment illustrated in FIG. 22, insertion end 216 isbounded on three sides by tapered surfaces 218, 220, and 221. While notspecifically illustrated in FIG. 22, insertion end 216 also can bebounded by a fourth tapered surface opposite tapered surface 220.Alternatively, opposite tapered surface 220, insertion end 216 can abutconvex surface 217.

Tool engaging end 222 is opposite of insertion end 216 on crescentshaped body 211. As with other preferred embodiments of the implants foruse with the present invention, tool engaging end 222 can include avariety of recesses, receptacles, grooves, slots, projections, and othersupporting members to engage corresponding surface features on animplant holder. In the preferred embodiment illustrated in FIG. 22, toolengaging end 222 includes central opening 224. Central opening 224 isprovided for slidably receiving a pin or a rod extension on an implantholder. Preferably, central opening 224 is provided with internalthreads for threadedly engaging a threaded pin or rod extension on animplant holder. Central opening 224 can extend over about 50% throughbody 211, more preferably central opening extends greater than about 80%through body 211. Most preferably, central opening 224 extends throughbody 211 of implant 210 so that an inserted pin or rod extension extendsthrough or to insertion surface 216. In preferred embodiments, centralopening 224 contains a uniform cross-sectional area throughout. It isunderstood that in alternative embodiments central opening 224 caninclude segments with different diameters and/or taper from toolengaging end to insertion end 216 to receive a pin or rod extension ofan implant holder that has the corresponding segment(s) or taper. (See,for example, the rod extension 246 in FIG. 32 a.) It is depicted in FIG.22 that central opening 224 extends through the recessed area 219defined by concave surface 215; however, it is understood thatalternative embodiments of implant 210 may provide a central opening 224that extends through or part way through implant 210 without accessingthe recessed area 219.

Yet another embodiment of an implant holder is depicted in FIGS. 23-24.Implant holder 240 includes extension 243, handle 241, shaft 242, andgripping head 244. Shaft 242 defines a longitudinal axis 247. Grippinghead 244 includes a first surface 250 for abutting and impacting thetool engaging end 222 to drive implant 210 into a prepared cavity. Thus,the implant holder not only releasably secures an implant, but alsoprovides a means for impacting the implant into a preformed cavity.Preferably, first surface 250 is roughened to better secure engagedimplant 210. Gripping head 244 also includes a holder extension 248adjoining first surface 250 at corner 252 at an included angle 253 ofabout 90°, preferably orthogonal to the direction of impaction orinsertion. However, in alternative embodiments, holder extension 248 canabut the first surface 250 and form an included obtuse angle 253 betweenthe first surface and the holder extension. Alternatively, the holderextension 248 can abut the first surface 250 and form an acute includedangle 253 between the first surface and the holder extension. (See, forexample, inclined surface 162 in FIG. 17 a.) It is understood that theangle between the first surface and holder extension 248 can be providedto frictionally secure abutting surface 226 and tool engaging end 222 onimplant 210. Thus, holder extension 248 can be adapted to inhibitlateral movement of the implant as it is impacted in the cavity.

Gripping head 244 also includes first rod extension 246. First rodextension 246 can include external threads for engaging internal threadsin a tool receiving recess in an implant. Preferably, rod extension 246is radiopaque to provide an X-ray indicator of the location of theimplant during surgery. Extension rod 246 can be fixedly mounted ontofirst surface 240. Alternatively, shaft 242 disposed between grippinghead 244 and handle 241 can be, but is not required to be, hollow forreceiving holder extension 248. Extension rod 246 can extend through anaperture (not shown) on surface 244 to be received within shaft 242. Inyet another alternative embodiment, first surface 250 can include asecond rod extension 245. Second rod extension 245 is adapted to receivefirst extension rod 246 therein so extension rod 246 is in communicationwith shaft 242.

Shaft 242 can include extension 243 for extending extension rod 246through first surface 250. For example, the end of extension rodreceived within shaft 242 can include external threads that engageinternal threads of extender 243. Twisting extender 243 causes extensionrod to travel in a longitudinal direction parallel to the longitudinalaxis 247 through shaft 242.

When the implants described in this present invention are inserted intoa intervertebral space, the recessed areas defined by curved surfaces onthe implants and the adjoining surfaces of the adjacent vertebra form achamber or depot for osteogenic material. (See FIG. 11.)

The recessed areas defined by curved surfaces of the implants describedin the present invention can be packed with any suitable osteogenicmaterial. The implants can be packed with osteogenic material prior toimplantation, or the osteogenic material may be inserted into thechamber or depot in the intervertebral space after one or two of theimplants have been inserted. In a preferred embodiment, the osteogeniccomposition substantially fills the recessed areas defined by theimplants so that the osteogenic composition will contact the endplatesof the adjacent vertebrae when the implant is implanted within thevertebrae. When “spongy” osteogenic material such as cancellous bonetissue is used, the cancellous tissue can be compressed into therecessed area or chamber to ensure sufficient contact with adjacentendplates. This provides better contact of the composition with theendplates to stimulate bone ingrowth.

Any suitable osteogenic material or composition is contemplated,including autograft, allograft, xenograft, demineralized bone, andsynthetic and natural bone graft substitutes, such as bioceramics andpolymers, and osteoinductive factors. The terms osteogenic material orosteogenic composition used herein broadly include any material thatpromotes bone growth or healing including autograft, allograft,xenograft, bone graft substitutes and natural, synthetic and recombinantproteins, hormones and the like.

Autograft can be harvested from locations such as the iliac crest usingdrills, gouges, curettes, and trephines and other tools and methodswhich are well known to surgeons in this field. Preferably, autograft isharvested from the iliac crest with a minimally invasive donor surgery.The osteogenic material may also include bone reamed away by the surgeonwhile preparing the endplates for the spacer.

Advantageously, where autograft is chosen as the osteogenic material,only a small amount of bone material is needed to pack the chamber. Theautograft itself is not required to provide structural support as thisis provided by the spacer. The donor surgery for such a small amount ofbone is less invasive and better tolerated by the patient. There isusually little need for muscle dissection in obtaining such smallamounts of bone. The present invention therefore eliminates or minimizesmany of the disadvantages of employing autograft to provide structuralsupport in the fusion procedure.

Natural and synthetic graft substitutes which replace the structure orfunction of bone are also contemplated for the osteogenic composition.Any such graft substitute is contemplated, including for example,demineralized bone matrix, mineral compositions, and bioceramics. As isevident from a review of An Introduction to Bioceramics, edited by LarryL. Hench and June Wilson (World Scientific Publishing Co. Ptd. Ltd.,1993, volume 1), there is a vast array of bioceramic materials,including BIOGLASS®, hydroxyapatite, and calcium phosphate compositionsknown in the art which can be used to advantage for this purpose. Thatdisclosure is herein incorporated by reference for this purpose.Preferred calcium compositions include bioactive glasses, tricalciumphosphates, and hydroxyapatites. In one embodiment, the graft substituteis a biphasic calcium phosphate ceramic including tricalcium phosphateand hydroxyapatite.

In some embodiments, the osteogenic compositions used in this inventioncomprise a therapeutically effective amount to stimulate or induce bonegrowth of a bone inductive or growth factor or protein in apharmaceutically acceptable carrier. The preferred osteoinductivefactors are the recombinant human bone morphogenetic proteins (rhBMPs)because they are readily available and do not contribute to the spreadof infectious diseases. Most preferably, the bone morphogenetic proteinis a rhBMP-2, rhBMP-4 or heterodimers thereof.

Recombinant BMP-2 can be used at a concentration of about 0.4 mg/ml toabout 1.5 mg/ml, preferably near 1.5 mg/ml. However, any bonemorphogenetic protein is contemplated including bone morphogeneticproteins designated as BMP-1 through BPM-13. BMPs are available fromGenetics Institute, Inc., Cambridge, Mass., and may also be prepared byone skilled in the art as described in U.S. Pat. Nos. 5,187,076 toWozney et al.; 5,366,875 to Wozney et al.; 4,877,864 to Wang et al.;5,108,922 to Wang et al.; 5,116,738 to Wang et al.; 5,013,649 to Wang etal.; 5,106,748 to Wozney et al.; and PCT Patent Nos. WO93/00432 toWozney et al.; WO94/26893 to Celeste at al.; and WO94/26892 to Celesteet al. All osteoinductive factors are contemplated whether obtained asabove or isolated from bone. Methods for isolating bone morphogeneticprotein from bone are described in U.S. Pat. No. 4,294,753 to Urist andUrist et al., 81 PNAS 371, 1984.

The choice of carrier material for the osteogenic composition is basedon biocompatibility, biodegradability, mechanical properties, andinterface properties as well as the structure of the load-bearingmember. The particular application of the compositions of the inventionwill define the appropriate formulation. Potential carriers includecalcium sulphates, polylactic acids, polyanhydrides, collagen, calciumphosphates, polymeric acrylic esters, and demineralized bone. Thecarrier may be any suitable carrier capable of delivering the proteins.Most preferably, the carrier is capable of being eventually resorbedinto the body. One preferred carrier is an absorbable collagen spongemarketed by Integra LifeSciences Corporation under the trade nameHelistat® Absorbable Collagen Hemostatic Agent. Another preferredcarrier is a biphasic calcium phosphate ceramic. Ceramic blocks arecommercially available from Sofamor Danek Group, B.P. 4-62180Rang-du-Fliers, France, and Bioland, 132 Rou d Espangne, 31100 Toulouse,France. The osteoinductive factor is introduced into the carrier in anysuitable manner. For example, the carrier may be soaked in a solutioncontaining the factor. One preferred embodiment contemplates use ofOSTEOFIL® allograph paste sold by Regeneration Technologies, Inc. Theallograph paste can be supplemented with a local autograft obtained fromthe cutting operation.

The present invention also includes instrumentation for preparing theintervertebral space between adjacent vertebrae for receiving an implantand for inserting the implant into the prepared space. Use of theimplants in accordance with the present invention restores the discheight, restores segmental alignment and balance, protects nerve roots,restores weight bearing to anterior surfaces, and immobilizes theunstable degenerated intervertebral disc area. The spacers of thispresent invention may be conveniently implanted with known instrumentsand tools, although improved instruments are provided that arespecifically adapted for the procedure. Any instrument that will firmlyhold the implant and permit the implant to be inserted is contemplated.Preferably, the instrument will be adapted to compensate for the openstructure of the spacers of this invention.

It is also provided with the present invention instruments for using andinserting the implants described herein. Specific instruments includebox chisels, impact or slap hammers, shavers, retractors, detractors,scrapers such as round scrapers, plain scrapers, rotatable scrapers orcutters, toothed scrapers and bone loaders. In addition, there isprovided a protective sleeve illustrated in FIG. 36 for use in guidedsurgical procedures.

In one aspect of the invention, a novel chisel is provided. The novelchisel for preparation of the preformed cavity in the intervertebraldisc space is depicted in FIGS. 25 through 25 d. Box chisel 260 includesa handle 262 having an engagement hole 263 adapted for attachment of animpacting tool such as a slap hammer shown in FIG. 27. In addition, boxchisel 260 includes shaft 264 extending from handle 262 and connectingwith cutting head 266. Shaft 264 defines a longitudinal axis 261.Cutting head 266 includes first arm 267 and opposing second arm 269extending from shaft 264 substantially parallel to longitudinal axis261. Upper cutting blade 268 and opposing lower cutting blade 270 aredisposed between first and second arms 267 and 269. First arm 267 andsecond arm 269 define internal cavity 276 for receipt of bone chips andcutting debris. One or both of first arm 267 and second arm 269 includeindex markings 274, which indicate the depth of cut for the box chisel,thus allowing the surgeon to determine how deeply he/she has cut intothe intervertebral space.

Non-cutting edge 273 is attached to first arm 267. Similarly,non-cutting edge 272 is attached to first arm 269. Non-cutting edges 273and 272 are positioned to extend distally beyond cutting blades 268 and270 in a direction parallel to the longitudinal axis. Referring to FIGS.25 b-c, non-cutting edge 273 includes an upper guide portion 296 and alower guide portion 298 extending at least partially beyond the cuttingedges. Similarly, non-cutting edge 272 includes identical upper andlower guide portions. The guiding portions contact the bone surfaceprior to the cutting edges 268 and 269. Preferably the non-cutting edges273 and 272 of the adjacent vertebrae are rounded to follow the interiorsurfaces of the opposing endplates of adjacent vertebrae. Thus, therounded non-cutting edges follow along the surfaces of endplates andcenter the box cutter within the disc space and the included upper andlower cutting blades 268 and 270 between the two endplates. When the twocutting blades are centered between the opposing endplates, the bladescut equal amounts of bone from each endplate and are prevented fromcreating a potential offset opening between the endplates, resulting inimproper implant placement and excess bone removal, which could increasethe risk of implant interface subsidence.

Attachment hole 263 in handle 262 of box chisel 260 is provided forattachment of an impact or slap hammer as depicted in FIG. 27. Impacthammers are well known in the art, and attachment hole 263 can beprovided for attachment to any of the known impact hammers for use withthe present invention. In preferred embodiments, slap hammer 310includes threaded end 320. Threaded end 320 is threadedly engaged ininternal threads in 263. Slap hammer 310 includes weight 316 that slideson shaft 314. Use of a slap hammer in accordance with this inventionallows for controlled force impacting cutting tool and implants. Theslap hammer also provides a means for removal of impacted surgical toolssuch as the chisel after cutting.

Referring now to FIGS. 25 b-d, in use box chisel cutting head 266 ispositioned in substantial alignment with a space 279 between adjacentvertebrae endplates 277 and 278. Non-cutting edges are inserted intospace 279 with guiding portions 296 and 298 engaging endplates 277 and278. Cutting head 266 is then advanced, by use of a slap hammer ifnecessary, with blades 268 and 270 removing the tissue of endplates 277and 278, respectively, disposed between the guide portions and theblades.

There is also provided in the present invention a novel retractorassembly as depicted in FIGS. 28-30. Nerve retractor assembly 330includes retractor handle 346, retractor 340, having a channel 352 forreceiving retractor blade 342. Channel 352 of retractor 340 is providedin a shape to minimize the amount of retraction of the neural structurenecessary to perform the procedures yet provide the surgeon with anunobstructed view of the intervertebral space. Channel 352 and retractorblade 342 are illustrated in FIGS. 28, 30, and 30 a as having agenerally concave shape. It is also considered within the scope of thepresent invention to provide channel 352 and retractor blade 342 inalternative shapes to meet specific needs to gain access to a surgicalsite.

Nerve retractor assemble 330 also includes at least one, preferably two,supporting members 331 and 333 positioned on opposing sides of channel352. Preferably, channel 352 includes at least one, preferably two,enlarged edges 347 and 349. Enlarged edges 347 and 349 can be adaptedfor receiving pin drive shaft 334. In addition, enlarged edges 347 and349 are adapted to receive and hold retractor blade 342. Retractor blade342 may be inserted from the top portion of channel 352 adjacent stop orshoulder 354 and slidably advanced toward distal end 351. Blade 342 isretained in place by enlarged edges 347 and 349, as well as surface 358.Retractor blade 342 further includes a distractor tip 344 sized to beinserted into a disc space to achieve or maintain distraction. It willbe understood that the width of tip 344 may be varied depending on theamount of distraction desired. Moreover, while pins 336 and 338 aredisclosed for maintaining the position of the retraction assembly, it iscontemplated that the engagement of retractor blade 342 in the discspace may be sufficient to hold the retraction assembly without the useof pins 336 and 338.

In alternative embodiments, pin 336 includes threads for threadingengagement in internal threads (not shown) of supporting member 349.Thus, pin 336 can be anchored to the channel of retractor 340. Pin 336includes pin driver handle 332, and pin driver shaft 334, which caninclude a lower portion which is slidably engaged in support member 331.Pin 336 includes at its distal end a tissue engagement end 337. A secondpin 338 can be mounted on a second supporting member 333. Aftermanipulation of the spinal structures using retractor blade 342 andretractor 340 to provide sufficient room to proceed with the PLIFoperation, tissue engaging end 337 of pin 336 is forcibly inserted intotissue such as bone to secure the retractor blade and the retractedneural structures. Alternatively, the second pin 338 can be used toinitially position and secure one side of nerve retractor assembly 330relative to the nerve structure. After the pin has been used to secureone side of the retractor, the retractor can be used to engage andmanipulate the selected nerve structure. After the nerve structure hasbeen sufficiently retracted, a second pin is forcibly inserted intotissue.

Retractor blade 342 is provided in a shape that can be nested in channel352 to ensure that the surgeon has an unobstructed view of the surgicalsite. Retractor blade 342 includes retractor tip 344 opposite stop 343.Stop 343 is inserted into opening 341 on retractor 340. Preferably, stop343 extends through opening 341 and engages shoulder 354 to secureretractor blade to retractor 340.

There is also provided in the present invention a distractor as depictedin FIGS. 31 and 31 a. Distractor 370 includes coupling 372 attached toone end of shaft 374 and a distractor head 376 disposed oppositecoupling 372 on shaft 374. Distractor head 376 is substantially in theform of a wedge shape, wherein distractor tip 379 forms the apex of thewedge. Preferably, distractor tip 379 contains a blunt edge. Distractorhead 376 includes large side 380 and a corresponding large side opposite380 to form the large side of a wedge. The large side of distractor head376 is defined as having a length illustrated by reference line 384.Similarly, small side 382 and corresponding side opposite 382 form theshort or small side of the wedge having a width illustrated by referenceline 386. Furthermore, the detractor head includes a series of indexmarkings 378 which index the depth the retractor is inserted intotissue.

Additional cutting instruments are provided for use with the presentinvention. For example, shaver 280 illustrated in FIGS. 26 and 26 a isprovided with a cutting head 286, shaft 284, and handle 282. Handle 282includes a receptacle 283 for attachment of a slap hammer. Cutting head286 includes upper shaving blade 288 and lower shaving blade 290provided between first arm 287 and second arm 289. Upper and lowershaving blade 288 and 290 are orthogonal to first and second arms 287and 289 such that when the upper or lower shaving blade 288 or 290 orboth are raked across tissue surfaces, the blades cut or scrape away aportion of tissue surface. Cutting head 286 also includes a series ofindex markings 294 to determine the depth of the scraper head in tissue.

Round scraper 390 illustrated in FIGS. 32-32 f is provided for use withthe present invention. Round scraper 390 includes shaft 402 and scraperhead 392. Shaft 402 defines a longitudinal axis 391. Scraper head 392includes a first arm 393 and a second arm 395. Shaft 402 includes atapered neck 403. First arm 393 and second arm 395 define a cavity 398for receipt of cutting debris. Attached to first and second arm 393 and395 are rounded scraper edges 394 and 396. First arm 393 and second arm395 are attached to curved tip 404. Rounded scraper edges 394 and 396are backward-facing cutting edges, which can cut bone or other tissue asthe round scraper 390 is withdrawn from the disc space. Round scraperedges 394 and 396 are provided to allow simultaneous cutting on opposingsurfaces of adjacent vertebral bodies. First arm 393 includes an uppersurface 397 and a lower surface 400. Upper surface 397 and lower surface400 are substantially flat. Second arm 395 includes similar structures.Upper surface 397 and/or lower surface 400 allow for controlled scrapingof the disc space by contacting either the upper or lower vertebralbody. Furthermore, the flat upper and lower surfaces 397 and 400 andtapered neck 403 are adapted to provide enhanced viewing of the discspace. It is important to be able to view the disc space whilepositioning the round scraper 390 in the disc space to remove bonytissue. Round scraper 390 is provided for preparing a bottom of thepreformed cavity for proper seating of implants as depicted in thepresent invention.

There is also provided in accordance with the present invention a planescraper 410 illustrated in FIGS. 33 through 33 c. Plane scraper 410includes scraper head 412. Scraper head 412 is adapted to provide aplurality of plane scraper blades 414 and 416. Plane scraper blades 414and 416 are integrally attached to first arm 415 and second arm 417. Oneor both of first arm 415 and/or 417 include index markings 418 toindicate the depth the plane scraper is inserted into the cavity. Firstand second arms 415 and 417 define a cavity 420 for receipt of bonecuttings and debris.

As shown in FIG. 34, there is also provided in accordance with thepresent invention rotatable cutter 430. Cutter 430 includes handle 432,shaft 434, and cutter head 436. Cutter head 436 includes first cuttingarm 437 and second arm 439. First cutting arm 437 and second cutting arm439 are spaced apart and define a cavity 448 therebetween for receipt ofcutting debris. First cutting arm 437 includes at least two cuttingblades. For example, FIG. 34 a depicts cutting arm 437 having a firstcutting blade 438 and opposite second cutting blade 440. First andsecond cutting blades extend longitudinally and are positioned to lieparallel to the longitudinal axis of rotatable cutter 430. Similarly,second cutting arm 439 is provided with a first cutting blade 442 and asecond cutting blade 443. Rotatable cutter 430 is provided for use in adisc space to cut adjacent endplates of adjacent vertebrae by a twistingthe cutter. As with other instruments, the cutting head includes indexmarks 441 to indicate the depth the rotatable cutter is inserted intotissue.

Referring to FIG. 35, toothed scraper 460 is provided in accordance withthe present invention. Toothed scraper 460 includes handle 462, shaft464, shaped flat distal end 466, and cutting head 468. Cutting head 468includes a plurality of scraper edges, each scraper edge having a seriesof teeth 471. In preferred embodiments, scraper head 468 includes firstscraper edge 470 and second scraper edge 472. Scraper head 468culminates in a curved distal end 474. As with other instrumentsprovided in accordance with the present invention, cutting head 468includes index markings 476 to indicate the depth the cutter is insertedinto tissues.

A preferred embodiment of protective guide sleeve 510 is illustrated inFIG. 36. Protective sleeve 510 includes hollow body 512. In preferredembodiments, hollow body 512 is provided in the form of a hollowrectangular tube. Hollow body 512 includes a seating end 516, which isopen and provides access to the interior of hollow body 512. Hollow body512 also includes an opposite end that branches into a first distractorfin 518 and second distractor fin 520 extending from end 517. Firstdistractor fin 518 is provided with inclined surface 526, which tapersto reduce the width of distractor fin 518. Distractor fin 518furthermore culminates in a first curve tip 522. Second distractor fin520 also includes an inclined surface 528 and culminates in curve tip524. Positioned between the seating end 516 and first and seconddistractor fins 518 and 520 is viewing aperture 514. Viewing aperture514 is provided for visualization of the interdisc space and viewing theindex marks on the instruments that are inserted through the interiorcore of hollow body 512. Use of protective sleeve 510 allows a surgeonto minimize incised area and exposure of internal tissue duringposterior lumbar interbody fusion surgical procedures. The protectivesleeve 510 provides protection for neural structures. Furthermore,seating end 516 of protective sleeve 510 provides a surface for engagingdepth stops on surgical instruments to control cutting bony surfaces andcountersinking implants.

A number of surgical instruments are illustrated in FIGS. 37 a-40 c thatcan be used in conjunction with guide sleeve 512. These instrumentsinclude many of the same features, benefits, and aspects as have alreadybeen disclosed in the above description. In addition, these instrumentsinclude additional features and objects. These instruments are adaptedto be received within the interior region of guide sleeve 512. Ingeneral, these surgical instruments include a shaft attached to asurgical head adapted to be received within the interior region of aguide sleeve.

Yet another embodiment of a box chisel is illustrated in FIGS. 37 a-38.Similar to the embodiment depicted in FIG. 25, chisel 550 comprises acutting head 551 that includes first non-cutting edge 554, secondnon-cutting edge 556, an upper cutting blade 558, and a lower cuttingblade 560. Cutting head 551 includes internal cavity 557. Chisel 550further includes a shaft 552 that is adapted to be received within theinterior region 513 of protective guide sleeve 510 as illustrated inFIG. 38. Depth stop 562 is mounted on shaft 552 to prevent the chiselfrom cutting deeper than a predetermined depth by contacting seating end516 on protective sleeve 510. In a preferred embodiment illustrated inFIG. 38, depth stop 562 is threadedly mounted on shaft extension 564 sothat rotation of depth stop 562 about the shaft adjusts the depth ofcut. Depth indicator marks 566 on shaft extension 564 indicate the depththe chisel will cut when depth stop 562 has contacted seating end 516.

Referring now to FIGS. 39 a-39 f, another embodiment of an implantholder is illustrated. The implant holder 570 includes a gripping head572, shaft 574, and handle 576. As with other embodiments of the implantholders described for use with the present invention, implant holder 570releasably secures and impacts an implant into a preformed cavity.Gripping head 572 includes structural features for both securelygripping the implant and for driving the implant. For example, in thepreferred embodiment illustrated in FIGS. 39 e and 39 f, gripping head572 includes a roughened impacting surface 577. Roughened impactingsurface 577 is provided substantially orthogonal to the direction theimplant is impacted into the vertebral body. The roughened surfaceprovides frictional engagement with the tool engaging end of the implantand, in combination with a second structure such as a second surface578, inclined surface 579 or a shaft extension 580, secures the implantto the gripping head during the PLIF operation. Once the implant hasbeen driven into the vertebra body, the implant is released from thegripping head.

Yet another embodiment of the implant holder is illustrated in FIGS. 40a-40 c. Implant holder 590 includes griping head 591, shaft 592, depthstop 593, and handle 594. Gripping head 591 includes an impactingsurface 595. Preferably, impacting surface 595 is roughened or knurled.Gripping head 591 also includes a second surface 597, which issubstantially orthogonal to impacting surface 595. A third inclinedsurface 598 abuts opposite end of impacting surface 595 from secondsurface 597. Shaft extension 599 protrudes through impacting surface 595to be received within shaft 592. Handle 594 includes extender 600, whichis rotatably mounted on handle 594. In preferred embodiments, shaftextender 599 extends through shaft 592 and handle 594 and includesexternal threads that are matingly received in internal threads on shaft592 or handle 594. Gripping head 591 includes structural features forboth securely gripping the implant and for driving the implant intointervertebral space. For example, impacting surface 595, in combinationwith a second surface 597 and/or incline surface 598, secures theimplant to the gripping head. Preferably, shaft extension 599 matinglyengages in a tool-engagement recess on an implant. In preferredembodiments, shaft extension 599 is radiopaque and extends throughimplant body to or through the insertion end. Radiopaque shaft extension599 provides a means for viewing the seating of an implant duringsurgery via radiography.

Implant holder 590 can be used with protective guide sleeve 510.Gripping head 591 and shaft 592 can be adapted to be slidably receivedwithin the interior region 513 of guide sleeve 510. Depth stop 593 onimplant holder 590 is adapted to engage or contact the seating end 516on guide sleeve 510.

In one preferred embodiment, implant holder 590 includes shaft 592,which is provided with a square or rectangular cross-section and adaptedto be matingly received with a square or rectangular protective guidesleeve. Mating engagement of implant holder 590 within protective sleeve510 correctly centers implant holder 590 and a secured implant in theprepared vertebral space.

Depth stop 593 can be provided on shaft 592 in a fixed position or avariable position. Varying the position of depth stop 593 on shaft 593allows for depth control during impaction of implant into the preparedvertebral space.

There is also provided in accordance with the present invention a bonegraft loader 670, illustrated in FIGS. 41 and 42. Bone graft loader 670includes plunger 672, depth stop 674, and pivot plate 678 pivotallymounted with pivot pin 676 relative to loader shaft 680. Loader shaft680 includes a first wall 688, a second, bottom surface 689, aninsertion end 686, and a second end 687. In preferred embodiments,loader shaft 680 also includes third wall 691 and fourth wall 692 shownin dashed lines, i.e., partly cut away. Fourth wall 692 opposite firstwall 688 includes opening 682 proximal to mounting surface 690 on pivotplate 678. Plunger 672 includes a first end 693 that is positionedwithin loader shaft 680. Furthermore, plunger 672 is adapted to beslidably received within loader shaft 680 such that plunger 672 isdisposed between pivot pin 676 and first wall 688. In a first position,first end 693 of plunger 972 is proximal to depth stop 674 and disposedwithin loader shaft 680 between pivot pin 676 and first wall 688. In asecond position, plunger 672 is proximal to insertion end 686 withinloader shaft 680 and disposed between pivot plate 678 and first wall688. Pivot plate 678 is pivotally mounted to loader shaft 680 with pivotpin 676 and disposed within loader shaft 680 in a first position in asubstantially a diagonal direction from pivot pin 676 to insertion end686. In a second position, pivot plate is disposed within loader shaft680 to lie substantially parallel to fourth wall 692. Pivot plate 678includes a mounting surface 690 for receiving osteogenic material 684.Opening 682 provides access to the interior of loader shaft 680 forreceipt of osteogenic material, which can be deposited on mountingsurface 690.

Referring additionally to FIGS. 43 a and 43 b, bone graft loader 670 canbe adapted to be slidably received within protective guide sleeve 510.Bone graft loader 670 can be used to pack osteogenic material, such asmorselized bone graft, into the intervertebral space. The morselizedbone graft can be packed either prior to insertion of an implant orsubsequent to insertion of an implant. Osteogenic material 684 is packedonto mounting surface 690 through opening 682 while plunger 672 is in afirst position distal from insertion end 686 of shaft 680. Bone graftloader 670 is then inserted into guide tube 510 position insertion end686 within the intervertebral space such that opening 682 opens eitherlaterally or medially within the intervertebral space. Plunger 672 ispushed into loader shaft 680 in a direction toward insertion end 686.When plunger 672 is thus disposed within loader shaft 680, pivot plate678 is disposed against fourth wall 692, and the osteogenic material 684is forced through opening 682 and into the intervertebral space.

Bone graft loader 670 can also be used to anteriorly position osteogenicmaterial in the intervertebral space. Plunger 672 is pushed part wayinto loader shaft 600 to dispose pivot plate 678 against fourth wall692. Osteogenic material can be inserted into loader shaft 680 throughopening 685 in insertion end 686. Insertion end 686 can be inserted intothe disc space preferably through protective guide sleeve 510. Forcingplunger 672 fully into loader shaft 680 forces the osteogenic materialinto the disc space.

Reference to donor bone is understood, for the purposes of the presentinvention, to include cortical bone, cancellous bone, and anycombination thereof, it also being understood that cortical bonetypically demonstrates greater structural integrity and is therefore apreferred material for fashioning load-bearing implants.

There also is provided a method of providing implants by a moreefficient use of donor bone. Current methodologies for providingcortical bone infusion implant spacers typically require cutting thespacer, usually in the form of a dowel, from the diaphysis of a longbone. Only a certain portion of the diaphysis bone wall is sufficientlythick to provide dowels with requisite strength to maintain theintervertebral space. For example, in a human femur, only about themiddle third of the diaphysis, where the shaft is narrowest and themedullary canal is well formed, has sufficient thickness and density tobe used to prepare cylindrical cortical dowels. The suitable portions ofthe diaphysis are sliced and then a cylindrical plug is cut from eachslice.

FIG. 44 a illustrates bone slice 610 viewed from above, which was cutfrom the diaphysis of a long bone. The medullary canal 612 liessubstantially in the center of the bone slice. Reference lines 616 and617, which outline a pattern for cylindrical dowel, are superimposed onbone slice 610. In FIG. 44 b the bone slice 610 is viewed from the side,and the pattern of the cylindrical bone dowel is defined by referencelines 616 and 617. The cylindrical bone dowels are cut from the boneslice, then machined to form a cylindrical dowel having the desiredshape and surface features. Most often the cylindrical dowels includethe medullary canal to provide a depot for osteogenic material andpromote fusion of the adjacent vertebrae. Much of the donor bone iswasted as is illustrated in FIGS. 45 and 46. Remnant 620, which includesa portion of the medullary canal 620, is often discarded. The presentinvention uses scraps such as remnant 621 to prepare implants. Forexample, remnant 620 may be used as a starting point to prepare acrescent-shaped implant according to the present invention. In FIG. 44c, a finished cortical bone dowel is illustrated. Cortical bone dowel622 is formed from bone slice 610.

Referring now to FIGS. 47 and 48, portions of long bones segments fromthe upper or lower third of the diaphysis of long bones are illustrated.Nearer to the end of the bone the slices are taken, the more irregularshaped the slices become. Cortical bone walls become much thinner or themedullary canal in these portions of the bone is not sufficientlycircular to be used to manufacture cylindrical dowels. Theabove-described bone segments are not suitable for the formation ofcylindrical dowels. However, these segments of the long bones can beused to form the implants shaped according to the present invention.Moreover, utilization of the teaching of the present invention may yielda greater volume of implants from the same amount of donor bone. Whileit is within the scope of this invention to use any suitable long bone,FIGS. 47 and 48 illustrate sections of humeral and tibial shafts. InFIG. 47, bone slice 640 is illustrated. A J-shaped implant 110 and twoimplants 10 having flat sides are superimposed in bone slice 640. In apreferred embodiment, three J-shaped implants can be prepared from asingle bone slice. Similarly, the bone segment of FIG. 48 may be dividedinto three crescent-shaped implants.

Use of these previously undesirable donor portions in accordance withthe present invention provides a more efficient use and conservation ofa limited and very valuable resource of cortical donor bone.

The present invention also includes a method for fusing adjacentvertebrae. The patient is placed on the operating table in the proneposition with lateral C-arm fluoroscopy. A midline incision provides theapproach and exposure of the interlaminar space and facet joints at theaffected level, which for this example is L4-5. The soft tissue exposureshould also include the pedicle entry zone at L4 with care taken to notdisrupt the facet caps or ligaments at L3-4. Exposure of the dura isaccomplished in a routine fashion with bilateral hemi laminectomy andmedial facetectomy with care to save the morselized bone ships removedduring this decompression. After the lateral dura and nerve roottraversing the L4-5 level has been exposed on both sides, the facetshould be removed laterally so that there is an adequate exposure to thedisc lateral to the L5 root bilaterally. An attempt to preserve somecomponent of the L4-5 facet complex should be made if possible. Theepidural veins are coagulated over the annulus or herniated disc, andany tethering of the L5 root is dissected to allow for sufficient medialretraction of the dura and L5 root.

A conventional discectomy is performed by incising the annulus withpreferably a 15 scalpel blade and removing this annulus with adiscectomy rongeur. This is done bilaterally, and then soft fragmentsfrom the intradiscal space or extruded fragments are removed with thediscectomy rongeur in a conventional fashion. Loose intradiscalfragments are removed both medially and laterally into a depth of about30 mm.

The remaining soft tissue or cartilaginous endplate coverings arescraped away from the endplate using the round scraper 390. Thisvigorous scraping or curettage of the soft tissue endplate material isdone starting medially under the midline and gradually working laterallyin a sweeping motion until the upper and lower cartilaginous endplateshave been cleared of the soft tissue. This is also performed bilaterallywith the intent to create satisfactory endplate surface to promotefusion of the endplate and morselized graft to be inserted in the discspace later in the procedure.

The disc space is then sequentially distracted until the original discspace height is obtained and the normal foraminal opening accomplished.This is done by inserting a 9 or 10 mm distractor 370 on one side,rotating it; then taking a distractor 370 1 mm larger and inserting itin the opposite side, rotating it; and then alternating sides until thedesired height is obtained. The largest distractors are left in the discspace in the distracted position while continued disc space preparationis performed on the opposite side.

Rotating cutter 430 is inserted into the non-distracted side and rotatedto remove residual intradiscal material and create a channel in thedorsal-most endplate, removing osteophytes and facilitating placement ofthe guide tube anchoring fins. The rotating cutter 430 is inserted intoa depth of about 30 mm, rotated, and carefully lifted out, removing thesoft tissue from the disc space. After using this on the left side, thedistractor 370 is removed from the right, inserted on the left,distracted, and then the rotating cutter 430 is used on the right sidein the same fashion. This is inserted and rotated until there is nofurther soft tissue removed from the disc space. After removing therotating cutter, the discectomy ronguers may also be re-inserted toremove residual soft tissue. At this point, the disc space and openingis ready to accept protective sleeve 510.

Using fluoroscopic guidance, appropriate size guide sleeve 510 isselected, and with the dura retracted using flat, bayoneted, dura andnerve root retractor, protective sleeve 510 is seated down into thelaminectomy defect and first distractor fin 518 and second distractorfin 520 are anchored into the disc space. Using the mallet, the guidesleeve is then impacted securely into the laminectomy opening withcaution not to trap dura or the upper traversing root under theprotective sleeve end 517. Once this has been seated on the disc spaceand the seating confirmed using fluoroscopic guidance, distractor 370 isremoved from the opposite side, and the nerve root retractor is liftedout as well.

The appropriate box chisel 550 is then inserted into the guide tube andwith the slap hammer or the mallet is impacted down into the disc space,cutting the tract in the endplate to accept the bone graft. This is doneusing fluoroscopic guidance to ensure that the upper cutting blades 558and lower cutting blades 560 enter the disc space and traverse in aparallel fashion to the endplates. The depth of the chisel may beadjusted by rotating depth 562 stop at the top of chisel 550. Once thechisel has been impacted to the desired depth, preferably about 23-28mm, it is then removed using the slap hammer technique, carefullyremoving it from the disc space. After removal of the chisel, whoseinternal cavity 557 may also include disc and endplate material, thediscectomy rongeur is inserted down the guide tube to remove any furtherresidual soft tissue.

The side-loading morselized bone graft loader 670 is then loaded with analloquat of morselized autologous or autograft bone and then insertedinto the guide sleeve 510 with the side opening 682 aimed laterally.Once the bone graft loader 670 is fully inserted in the guide sleeve510, the piston 672 is impacted down the loader shaft 680 delivering themorselized bone laterally. The bone graft loader 670 is then removed inthis “delivered position,” the piston removed from the loader shaft 680,and the second alloquat of bone inserted in the bone graft loader. Thebone graft loader 682 is then again inserted and aimed with the opening602 aimed medially. When fully inserted, an alloquat of morselized boneis then delivered medially under the midline. The bone graft loader isonce again removed, and the disc space is ready to accept the structuralallograft.

The appropriate-sized implant 210 is then attached to implant holder570, and the shaft extension 580 is fully extended by turning extensionknob 582, seating the graft on the loader firmly. It is then placed inthe guide sleeve 510 and impacted into the disc space to the desireddepth. The shaft extension 580 is then unscrewed from the graft and thenimplant holder 570. The guide sleeve 510 is also then removed from discspace, and the discectomy and graft site inspected. The epidural spaceis then temporarily packed with gel foam for hemastasis, and the entireprocedure is again repeated on the opposite side.

After the interbody grafts have been securely placed and their locationconfirmed using fluoroscopy, the large rongeur is used to remove thedorsal aspect of the L5 facet joint at the transverse process on theleft side exposing the opening to the L5 pedicle. Using a pedicle probeand with fluoroscopic guidance, the trajectory or path of the pedicle isidentified, the pedicle probe is removed, and the appropriate-sized tapinserted down the pedicle, followed by the DYNA-LOK® pedicle screw. Thissame procedure is repeated at L4 with care taken not to disrupt thefacet joint or ligament at L3-4. The lateral aspect of the facet andtransverse process at the junction are removed with the rongeur followedby the probe, tap, and then pedicle screw. This is again repeated on theopposite side. When all four screws have been placed, the titanium plateis seated down over the pedicle screws. The residual morselized bonefrom the laminectomy and facet is packed laterally over the residualfacet joint and medical transverse processes and then the locking screwsare seated down onto the plate, and pedicle screws tightened to securethe plates to the pedicle screws. If necessary, a compressor is used toplace compression forces on the pedicle screws as the nuts are beingtightened down. After the nuts have been tightened, the epidural spaceis once again inspected for appropriate decompression of the L4 and L5nerve roots, hemastatis is obtained using the gel foam sponge, and thenthe wound is closed in layers after irrigating with vast tracentsolution. Care is taken to close the fascia securely and attach it tothe residual spinous process and interspinous ligament if possible.

It is understood to those skilled in the art that the above procedurecan be directed to a transforminal procedure using a far lateral PLIFapproach through the facet joint. Typically, the facet joint is removedto provide an approach to the disc space in an oblique orientationrelative to the posterior vertebral body. This provides access to thedisc space with minimal retraction of the dural structure and nerveroots.

While the invention has been illustrated and described in detail in thedrawings and the foregoing description, the same is considered to beillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

1. A spinal implant, comprising: an elongate bone portion formed from across-sectional bone slice taken from a diaphysis of a long bone havingan outer cortical bone wall surrounding an inner medullary canal, saidelongate bone portion having a longitudinal axis and including: a firstend portion; a second end portion arranged generally opposite said firstend portion; a first bone engaging surface; a second bone engagingsurface arranged generally opposite said first bone engaging surface; afirst sidewall extending between said first and second bone engagingsurfaces and including a recessed area disposed between said first andsecond end portions, said recessed area defined by a partial portion ofthe medullary canal of the long bone and defining a concave outersurface extending along said longitudinal axis between said first andsecond end portions from said first bone engaging surface to said secondbone engaging surface; and a second sidewall arranged generally oppositesaid first sidewall relative to said longitudinal axis, said secondsidewall extending between said first and second bone engaging surfacesand including a convex outer surface extending along said longitudinalaxis between said first and second end portions from said first boneengaging surface to said second bone engaging surface; and wherein saidconcave outer surface of said first sidewall extends generally parallelwith and is positioned opposite said convex outer surface of said secondsidewall to provide said elongate bone portion with an elongatecrescent-shaped outer cross-section in a plane including saidlongitudinal axis.
 2. A system including a pair of the spinal implantsof claim 1 wherein said pair of spinal implants includes a first implantand a second implant, said first and second implants positioned adjacentone another with said concave outer surface of said first implant facingsaid concave outer surface of said second implant with said concaveouter surfaces defining a chamber therebetween.
 3. The system of claim 2further comprising an osteogenic material disposed within said chamberdefined between said concave outer surfaces of said first and secondimplants.
 4. The system of claim 2 wherein said first and secondimplants are positioned such that said longitudinal axis of said firstimplant lies at an angle oblique angle relative to said longitudinalaxis of said second implant.
 5. The implant of claim 1 wherein saidelongate bone portion has a generally rectangular cross-section in aplane including the longitudinal axis.
 6. The implant of claim 1 whereineach of said first and second bone engaging surfaces is substantiallyplanar.
 7. The implant of claim 6 wherein each of said first and secondbone engaging surfaces includes ridges or teeth.
 8. The implant of claim6 wherein each of said first and second bone engaging surfaces iscrescent-shaped.
 9. The implant of claim 1 wherein said first and secondbone engaging surfaces are separated by a first height adjacent saidfirst end portion and by a second height adjacent said second endportion, wherein said first height is greater than the second height.10. The implant of claim 1 further comprising a first endwall extendingbetween said first and second bone engaging surfaces, wherein said firstendwall includes one or more engagement features adapted to engage animplant holder.
 11. The implant of claim 10 wherein said engagementfeatures comprise a recess or a projection configured to engage theimplant holder.
 12. The implant of claim 10 wherein said engagementfeatures comprise an opening extending through said first endwall tosaid concave outer surface of said first sidewall.
 13. The implant ofclaim 12 wherein said opening is threaded.
 14. The implant of claim 1wherein one of said first and second end portions comprises an insertionend, said insertion end being shaped to facilitate insertion into avertebral cavity.
 15. The implant of claim 14 wherein said insertion endis tapered to facilitate insertion into the vertebral cavity.
 16. Theimplant of claim 15 wherein said insertion end includes: a first taperedsurface extending from said first bone engaging surface; and a secondtapered surface extending from said second bone engaging surface; andwherein said first and second tapered surfaces are inwardly taperedtoward one another along said insertion end.
 17. The implant of claim 16wherein said insertion end includes a third tapered surface extendingfrom said convex outer surface of said second sidewall.
 18. The implantof claim 17 wherein said insertion end includes a fourth tapered surfaceextending from said concave outer surface of said first sidewall; andwherein said third and fourth tapered surfaces taper toward one anotheralong said insertion end.
 19. The implant of claim 15 wherein saidinsertion end includes: a first tapered surface extending from saidconvex outer surface of said second sidewall; and a second taperedsurface extending from said concave outer surface of said firstsidewall; and wherein said first and second tapered surfaces areinwardly tapered toward one another along said insertion end.
 20. Theimplant of claim 15 wherein said insertion end is bounded on at leastthree sides by tapered surfaces.
 21. The implant of claim 14 whereinsaid insertion end is bullet-shaped to facilitate insertion into thevertebral cavity.
 22. A method of forming a spinal implant, comprising:providing a long bone having a diaphysis; removing a cross-sectionalbone slice from the diaphysis of the long bone, the cross-sectional boneslice including an outer cortical bone wall surrounding an innermedullary canal having a length; cutting the bone slice along the lengthof the medullary canal and dividing the bone slice into a plurality ofbone slice segments, with each of the bone slice segments including apartial portion of the outer cortical bone wall and a partial portion ofthe medullary canal; and forming the spinal implant of claim 1 from oneof the plurality of bone slice segments, with the recessed area of thefirst sidewall defined by the partial portion of the medullary canal.23. The method of claim 22 further comprising forming the spinal implantfrom each of the plurality of bone slice segments obtained from a singlebone slice.
 24. The method of claim 22 wherein the cutting of the boneslice along the length of the medullary canal comprises dividing thebone slice into three bone slice segments, with each of the three boneslice segments including a partial portion of the outer cortical bonewall and a partial portion of the inner medullary canal.
 25. The methodof claim 24 further comprising forming the spinal implant from each ofthe three bone slice segments obtained from a single bone slice.
 26. Themethod of claim 22 further comprising forming a cylindrical bone dowelfrom one of the bone slice segments; and forming the spinal implant fromone of the remaining bone slice segments.
 27. A method of forming aspinal implant, comprising: providing a long bone having a diaphysis;removing a cross-sectional bone slice from the diaphysis of the longbone, the cross-sectional bone slice including an outer cortical bonewall surrounding an inner medullary canal having a length; cutting thebone slice along the length of the medullary canal and dividing the boneslice into a plurality of bone slice segments, with each of the boneslice segments including a partial portion of the outer cortical bonewall and a partial portion of the medullary canal; and forming anelongate bone portion from one of the plurality of bone slice segments,the elongate bone portion having a longitudinal axis and including: afirst end portion; a second end portion arranged generally opposite thefirst end portion; a first bone engaging surface; a second bone engagingsurface arranged generally opposite the first bone engaging surface; anda first sidewall extending between the first and second bone engagingsurfaces and including a recessed area disposed between the first andsecond end portions, the recessed area defined by the partial portion ofthe medullary canal and defining a concave outer surface extending alongthe longitudinal axis between the first and second end portions from thefirst bone engaging surface to the second bone engaging surface.
 28. Themethod of claim 27 further comprising forming the elongate bone portionfrom each of the plurality of bone slice segments obtained from a singlebone slice.
 29. The method of claim 27 wherein the cuffing of the boneslice along the length of the medullary canal comprises dividing thebone slice into three bone slice segments, with each of the three boneslice segments including a partial portion of the outer cortical bonewall and a partial portion of the inner medullary canal.
 30. The methodof claim 29 further comprising forming the elongate bone portion fromeach of the three bone slice segments obtained from a single bone slice.31. The method of claim 27 further comprising forming a cylindrical bonedowel from one of the bone slice segments; and forming the elongate boneportion from one of the remaining bone slice segments.
 32. The method ofclaim 27 wherein the elongate bone portion has a generally rectangularcross-section in a plane including the longitudinal axis.
 33. The methodof claim 27 wherein each of the first and second bone engaging surfacesis substantially planar.
 34. The method of claim 33 further comprisingproviding each of the first and second bone engaging surfaces with aplurality of ridges or teeth.
 35. The method of claim 27 wherein theelongate bone portion further includes a second sidewall arrangedgenerally opposite the first sidewall relative to the longitudinal axis,the second sidewall extending between the first and second bone engagingsurfaces and including a convex outer surface extending along thelongitudinal axis between the first and second end portions from thefirst bone engaging surface to the second bone engaging surface; andwherein the concave outer surface of the first sidewall extendsgenerally parallel with and is positioned opposite the convex outersurface of the second sidewall to provide the elongate bone portion withan elongate crescent-shaped outer cross-section in a plane including thelongitudinal axis.
 36. The method of claim 27 wherein the elongate boneportion further includes a second sidewall arranged generally oppositethe first sidewall relative to the longitudinal axis, the secondsidewall extending between the first and second bone engaging surfacesand including a substantially planar outer surface extending along thelongitudinal axis between the first and second end portions from thefirst bone engaging surface to the second bone engaging surface; andwherein the concave outer surface defined by the first sidewall ispositioned opposite the substantially planar outer surface of the secondsidewall relative to the longitudinal axis.
 37. The implant of claim 36wherein the first sidewall includes: a first substantially planar outersurface adjacent the first end portion and a second substantially planarouter surface adjacent the second end portion, each of the first andsecond substantially planar outer surfaces extending between the firstand second bone engaging surfaces; and wherein the concave outer surfaceextends axially between the first and second substantially planar outersurfaces.
 38. The method of claim 27 wherein the first and second boneengaging surfaces are separated by a first height adjacent the first endportion and by a second height adjacent the second end portion, whereinthe first height is greater than the second height.
 39. The method ofclaim 27 wherein the elongate bone portion further includes a firstendwall extending between the first and second bone engaging surfaces,wherein the first endwall includes one or more engagement featuresadapted to engage an implant holder.